Most popular with fingerprint verification devices vendors method used is the minutia based verification. This is also the oldest method used by the FBI and other government agencies and in other countries around the world. It is well established understood and standardized. There is an ANSI (American National Standards Institute ) standard for "Data Format for the Interchange of Fingerprint Information", describing a common format for interchange of minutia based fingerprint data. Minutia data represents four categories of fingerprint characteristic points: ridge ending, bifurcation, compound (trifurcation or crossover ) and type undetermined. Ridge ending occurs when a friction ridge begins or ends within the fingerprint and without splitting into two or more continuing ridges, and the ridge must be longer than it is wide. A bifurcation occurs when a ridge divides or splits to form two ridges that continue past the point of division for a distance that is at least equal to the spacing between adjacent ridges at the point of bifurcation. A compound type occurs either when there is trifurcation, which is when a single ridge splits into three ridges, or there is a crossover, i.e. when two ridges intersect each other. Finally when the minutia cannot be clearly categorized as one of the above three types it is designated as undetermined. Minutia based system, however, are pretty slow, and any defects in the input fingerprint image could generate false minutia. They are used predominantly in large fingerprint identification databases where input fingerprint data could be manually quality controlled and because minutia fingerprint data could be transferred between systems due to format standardization. They are also pretty expensive, which further limits their areas of application.
There are other systems, based on full image analysis. They perform complex two dimensional FFT's on the fingerprint data. Then in the frequency domain a two dimensional cross correlation is done between 2D-FFT of the fingerprint to be verified and the conjugate of the biocript image (or vice versa) and the cross correlation result is thresholded to determine if the images are similar. In some devices cross correlation is performed optically.
Those systems are usually much faster than the minutia based ones. However, the size of their template is usually much larger and they are not very suitable for large fingerprint data bases due to the nature of the verification process.
Both described systems are also very sensitive to finger placement on the fingerprint image scanner devices. Relatively small displacements or rotations of the finger could lead to false results.